The Smectic Rheology of a Polysiloxane Side Chain Liquid Crystalline Polymer

The rheology of a side chain liquid crystalline polymer (SLCP) with a polysiloxane backbone was investigated. The dynamic shear moduli of the SLCP in a smectic phase did not show the normal terminal behavior as the homogenous polymeric melts did, and instead, they tended to level off in the low frequency terminal zone. Time–temperature superposition failed for both dynamic moduli in the low frequency terminal zone and the departure from the superposition became more evident in the vicinity of smectic/isotropic transition. The plateau-like moduli in the terminal zone indicated the layer structure of the smectic phase. The steady shear viscosities of the smectic phase exhibited a shear thinning behavior over the shear rates investigated. The shear thinning was lost at low shear rates when the temperature passed the smectic/biphasic border. The shear viscosity and the dynamic moduli showed a divergence in the neighborhood of the smectic/isotropic temperature. The activation energies of the shear viscosity and the moduli were smaller than that of the SLCP with polymethacrylate backbone. The rheological behavior of the SLCP at low frequencies and low shear rates was dominated by the smectogen.